docs: def get_student_certificates(self, username, course_ids=None):
          """
          Returns an Certificates object with the user certificates
  
          Args:
              username (str): an edx user's username
              course_ids (list): a list of edX course ids.
  
          Returns:
              Certificates: object representing the student certificates for a course
          """
          # if no course ids are provided, let's get the user enrollments
          if course_ids is None:
              enrollments_client = CourseEnrollments(self.requester, self.base_url)
              enrollments = enrollments_client.get_student_enrollments()
              course_ids = list(enrollments.get_enrolled_course_ids())
  
          all_certificates = []
          for course_id in course_ids:
              try:
                  all_certificates.append(self.get_student_certificate(username, course_id))
              except HTTPError as error:
                  if error.response.status_code >= 500:
                      raise
  
          return Certificates(all_certificates)